PDP has persistently welcomed, entertained, joked uncritically, and normalized the exact attitudes, ideas, and motivations for this slaughter. He's made mass killings like the Holocaust a key part of his "comedy" for his young, impressionable audience for years and years. He's massively influential, and he's shared and advocated for white supremacists and their propagandists with all the vigor of a true believer.
This killer directly alludes to that influence. PDP has consistently mocked the idea of any responsibility on these points, through a multitude of situations where he megaphoned the bigoted hatred that drove this killing. He playfully chides any criticism of it.